1. Field of the Invention
The invention relates to an image-forming method and apparatus in which digital image data representing image information from one or more documents, is stored in a memory and read out of the memory to form images on copy sheets in a first image orientation or in a second image orientation rotated through 180.degree. with respect to the first orientation.
2. Discussion of Related Art
A method is known from U.S. Pat. No. 4,453,841, in which copy sheets can be provided with an image on the front and back. In these conditions, when processing copy sheets so transported through the image forming device that the longest peripheral side extends in the direction of transport, it is necessary that the image data for the front or back should be rotated through 180.degree. to ensure that the orientation of the image information is the same on the front and back of the sheet. This is effected by reading out of the memory in the reverse sequence the image data for that side of a copy sheet whose image data has to be rotated through 180.degree. or storing the same in the memory already in the reverse sequence. The latter option is the most attractive because, in that way, reading out of the memory for image forming purposes can always take place in the same direction irrespective of the orientation. However, in storing image data which is to be stored in the memory in the reverse sequence there is the problem that it is not possible to efficiently use the available memory space.
Since it is impossible to know beforehand how much memory space such image data will occupy, certainly if the image data is to undergo compression, the option chosen is to reserve a predetermined memory space which is ample enough on the basis of the least favorable situation in respect of data compression.